The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also accommodating a set of auxiliary actuating devices related to the operation thereof and ensuring various functions when the turbojet engine is operating or shut-down. These auxiliary actuating devices comprise, in particular, a mechanical thrust reverser system.
More specifically, a nacelle generally presents a tubular structure comprising an air inlet upstream of the turbojet engine, a mid-section intended to surround a fan of the turbojet engine, a downstream section accommodating the thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally ended by an ejection nozzle, the outlet of which is located downstream of the turbojet engine.
Modern nacelles are intended to accommodate a bypass turbojet engine capable of generating, via the blades of the rotary fan, a hot air flow (also called main flow) coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) which circulates outside of the turbojet engine through an annular channel, also called flow path, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected out from the turbojet engine from the rear side of the nacelle.
The role of a thrust reverser, during the landing of an aircraft, is to improve the braking capability thereof by redirecting forwards at least one portion of the thrust generated by the turbojet engine. In this phase, the thrust reverser obstructs the annular channel of the cold air flow and directs said cold air flow forward of the nacelle, consequently generating a counter-thrust which is added to the braking of the wheels of the aircraft.
The means implemented to make this reorientation of the cold air flow vary depend on the thrust reverser type. However, in all cases, the structure of a thrust reverser comprises movable cowls displaceable between, on the one hand, a deployed position in which they open in the nacelle a passage intended for the diverted flow, and on the other hand, a retracted position in which they close this passage. These cowls may fulfill a diverting function or simply an activation function of other diverting means.
In the case of thrust reverser with cascade vanes, also known as cascade-type thrust reverser, the reorientation of the air flow is performed by cascade vanes associated to thrust reverser flaps, the cowl having only a simple sliding function aiming to uncover or cover the cascade vanes. The thrust reverser flaps form blocking doors activated by the sliding of the cowling generally resulting in a closure of the annular channel downstream of the cascades so as to optimize the reorientation of the cold air flow.
Conventionally, the connection of the engine to the aircraft is performed by means of a support structure comprising two upper longitudinal beams, conventionally called 12 hours (or 12 o'clock) beams because of the position thereof at the top of the nacelle, two lower longitudinal beams, conventionally called 6 hours (or 6 o'clock) beams because of the position thereof in the lower portion of the nacelle, and a assembly having a substantially annular shape called front frame, actually formed of two front half frames each extending between said upper and lower longitudinal beams, and intended to be fastened to the periphery of the downstream edge of the casing of the fan of the motor.
The thrust reverser cascades are generally connected to each other by means of a thrust reverser rear frame. As shown in FIGS. 1a and 1b, such a rear frame 1 generally has a C-shaped (FIG. 1a) or L-shaped (FIG. 1b) section, so as to increase the inertia of the structure, and is provided with two ends each fitted with a fastening clevis 2 connected to the 12 hours beam and the other connected to the 6 hours beam. This frame has a fitting 3 for the passage of an actuating cylinder of the thrust reverser cascades in the direction of the thickness of the thrust reverser rear frame. Such a fitting imposes making a thrust reverser frame having a significant bulk in order not to weaken the structure of the thrust reverser rear frame, and thus deteriorating its characteristics of structural resistance to the stresses to which it is subjected during use. Therefore, besides a significant bulk, such a rear frame also has a significant weight. In some configurations, the cascades are directly connected to each other without the use of a rear frame. This solution has the drawback of shortening the effective surface of the cascades and requires elongating the cascades in order to have an equivalent effectiveness.
Consequently, techniques have been developed to make lighter rear frames while preserving a significant bulk so as to allow the realization of the fitting for the passage of the actuating cylinder of the thrust reverser cascades while deteriorating as less as possible the structural characteristics of the rear frames. These technologies consist in the use of materials such as composites.
Nevertheless, so far, these technologies have not provided the reduction of the bulk of the thrust reverser rear frame even though such a reduction might have multiple technical advantages.